Two explosions struck the Boston Marathon on Monday as runners crossed the finish line, with the Boston Police Department confirming two deaths and 23 injuries.

A federal law enforcement official confirmed to ABC News this was an intentional bombing, using small portable explosive devices. The Boston Police Department revealed via Twitter that a third incident took place at JFK Library. Though no certain connection to the marathon explosion has been made, police are treating the third incident as if they are related. The Boston Police department is asking for tips regarding the two explosions, that took place at 2:50 p.m. at the marathon finish line.

Boston police are looking for video of the finish line and as police stabilize the situation and scene, they are checking packages.

"Somebody's leg flew by my head," a spectator, who gave his name as John Ross, told the Boston Herald. "I gave my belt to stop the blood."

"I saw two explosions. The first one was beyond the finish line. I heard a loud bang and I saw smoke rising," Boston Herald reporter Chris Cassidy, who was running in the marathon, told the newspaper. "I kept running and I heard behind me a loud bang. It looked like it was in a trash can or something...There are people who have been hit with debris, people with bloody foreheads."

Boston firefighters found what they believe is an unexploded device after the blasts, a government official said, according to CNN's Joe Johns.